1. Field of the Invention
The present invention relates to an audio system for playing back recorded information by remote transmission and, more particularly, to an audio system for playing back recorded information by remote transmission wherein an output device such as a speaker installed at a location remote from an audio playback server can be operated using a keyboard, mouse, etc. attached to the server.
2. Description of the Related Art
A variety of audio information playback apparatuses for playing back digital audio signals from a recording medium, such as a magnetic tape, compact disc (CD), or digital versatile disc (DVD), and for reproducing the sound through speakers have been developed in the prior art, as disclosed, for example, in Japanese Unexamined Patent Publication Nos. H04-307470 and H08-96512.
An audio system for playing back sound information recorded on CDs can be taken as a representative example of the prior art audio playback apparatus. In this CD audio playback system, an audio playback server, a digital/analog (DA) conversion circuit, and speakers are connected. The audio playback server includes a CD audio playback processor IC, and outputs digital data, i.e., the audio signal read from the CD, along with an L/R channel discriminating stereo (R/L) signal associated with the audio signal and a clock signal for determining the input/output timing of the digital data.
The audio signal, the stereo signal, and the clock signal output from the audio playback server are input to the digital/analog (DA) conversion circuit. Here, the audio signal is converted into a stereo analog signal in accordance with the stereo signal and the clock signal, and is output to the speakers which reproduce the audio signal as sound.
In the above CD audio playback system, generally, the CD audio playback processor IC and the DA conversion circuit are integrated into a single package to reduce the cost. However, there are cases where output devices such as the speakers have to be installed at a location far away from the CD audio playback server; in such cases, the CD audio playback server is connected to the output devices via a local area network (LAN).
In the thus configured CD audio playback system, when such problems as S/N ratio and signal attenuation are considered, it would not be advantageous to transmit the analog output signal to the speakers by connecting the DA conversion circuit to the speakers over a long cable. One possible solution to this problem is to install the DA conversion circuit and the speakers separately from the audio playback server and to connect between the DA conversion circuit and the audio playback server by a long cable along which the signal can be transmitted in digital data form.
In that case, as the audio signal as the audio digital data, the stereo signal as the L/R digital data, and the clock signal as the system clock are each transmitted using a twisted-pair cable consisting of a pair of conductors, three twisted-pair cables (a total of six conductors) must be installed. If a bit clock is to be transmitted separately from the system clock, one more twisted-pair cable has to be added as a cable for transmitting the bit clock.
In this way, when transmitting digital data to the DA conversion circuit and the speakers located remotely from the audio playback server, at least three twisted-pair cables have to be installed. As a result, as the distance from the audio playback server to the speakers as the output devices increases, the cables connecting between them become longer, and hence there arises the problem that the cost increases.